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Indian Geotechnical Conference – 2010, GEO trendz December 16–18, 2010 IGS Mumbai Chapter & IIT Bombay

California Bearing Ratio, Evaluation and Estimation: A Study on Comparisons

Roy, T.K. Chattopadhyay, B.C. Roy, S.K. Sr. Lecturer Professor Professor e-mail: [email protected], [email protected] e-mail: ccbikash@ yahoo.co.in e-mail: sudip@ civil.becs.ac.in Department of Civil Engineering, Bengal Engineering & Science University, Shibpur, Howrah

ABSTRACT In India, California Bearing Ratio (CBR) value of is used often for design of flexible pavements. In practice, only limited number of such tests could be performed because of high unit cost and time required for such testing. As a result, in many cases, it is difficult to reveal detailed variations in the CBR values, over the length of . In such cases if the estimation of the CBR could be done on the basis of some tests which are quick to perform, less time consuming and cheap, then it will be easy to get the information about the strength of subgrade over the length of roads and also will be helpful and important specially for low volume roads being constructed under Pradhan Mantri Gram Sadak Yojana (PMGSY) scheme over different states of India presently, to develop large scale connections of rural India within a short period of time. By considering this aspect, a number of investigators in the past made their investigations in this field and developed different methods for determining the CBR value on the basis of results of low cost, less time consuming and easy to perform tests. In this study, attempts have been made to seek the validation of the predicted values of CBR determined by different method as per guidelines of IRC:SP:72-2007.

1. INTRODUCTION evaluation of CBR of subgrade on the basis of simple California bearing ratio (CBR) is an empirical test and and less time consuming tests may be necessary specially widely applied in design of flexible pavement over the in such types of low volume roads. In the past, several world. This method was developed during 1928-29 by the attempts have been made to predict CBR by using different California Highway Department. Use of CBR test results methods. Karunaprema and Edirisinghe (2002) and for design of roads, introduced in USA during 2 nd World Nuwaiwu et al. (2006) performed the investigations for War and subsequently adopted as a standard method of prediction of CBR from the Dynamic Cone Penetration design in other parts of the world, is recently being (DCP) value and plasticity modulus. A study to check the discouraged in some advanced countries because of the validity of available correlations between CBR and other imperialness of the method (Brown, 1996). In addition, properties of soils has been made by Roy et al. (2006). CBR test in laboratory requires a large sample and is Shukla and Kukalyekar (2004) have developed correlations laborious as as time consuming. Furthermore, the of CBR with the compaction characteristics for the results sometimes are not accurate due to poor quality of compacted fly ash. Recently Srinivasa Rao (2004) skill of the technicians testing the soil samples in the developed a correlation between CBR and Group index laboratory. All these problems may result in serious delay based on tests on about 150 soil samples covering a wide in the progress of the project and ultimately it may lead to range of soil types. In this paper, an attempt has been made escalation of the project cost. Government of India launched to make the comparison between the predicted and the a prestigious project namely Pradhan Mantri Gram Sadak experimental values of CBR as per the guidelines of Yojana (PMGSY) for providing the connectivity to the IRC:SP:72-2007 for different projects of PMGSY. unconnected rural areas. In this project, the designers have 2. AVAILABLE METHODS FOR PREDICTING to use the CBR value of soil for determining the thickness CBR of the where soaked/unsoaked CBR of soil samples to For the design of new roads, the CBR value may be be used as subgrde to be determined in the laboratory. So 20 T.K. Roy, B.C. Chattopadhyay and S.K. Roy predicted as per IRC:SP:72-2007 by using the presumptive 3. METHODOLOGY AND DISCUSSION chart on the basis of tests which gives For checking the applicability of the above cited methods typical presumptive design CBR values for soil samples for predicting CBR, reported different properties like Liquid compacted to maximum dry density at optimum moisture limit (LL), Plastic limit (PL), Plasticity index (PI), Grain content and soaked under water for 4 days as shown in the size distribution etc. of soils along with the soaked CBR Table 1. have been collected from the Detailed Project Report (DPR) Another method is by using Nomograph based on wet of different roads project of different district of West Bengal data, for estimating soaked CBR values on under PMGSY and shown in the Table 2. List of the places samples compacted to Proctor density as shown in the of the collected soil samples are furnished below: Figure 1. Sl.No.1: Deul to Basanti, at CH. 0.4 km, Kumargang Table 1: Typical Presumptive Design CBR Values Block, Dist.-Dakshin Dinajpur, W.B. Sl.No.2: Deul to Basanti, at CH. 1.10 km, Kumargang Description of IS Soil Typical Soaked Subgrde Soil Classification CBR Values (%) Block, Dist.-Dakshin Dinajpur, W.B. Sl.No.3: Dakshin Jamalpur to Fatepur, at CH. 4.00 km, Highly Plastic Clays Tapan Block, Dist.- Dakshin Dinajpur, W.B. CH, MH * 2-3 and Sl.No.4: 18 No Road to Chowtara, at CH. 2.00 km, Silty Clays and Sandy ML, MI Dhaniakhali Block, Dist.-Hooghly, W.B. 4-5 Clays CL, CI Sl.No.5: Birshimul more to Kantapukur, at CH. 1.00 km, Memari Block, Dist.- Bardhaman, W.B. Clayey and SC, SM 6-10 Sl.No.6: T-02 to Buranagar, at CH. 0.60 km, Bhangar- Silty Sands I Block, Dist.-South 24 Parganas, W.B. * Expansive clays like BC Soil may have a soaked CBR of less Sl.No.7: T-02 to Buranagar, at CH. 3.80 km, Bhangar- than 2% I Block, Dist.-South 24 Parganas, W.B. Sl.No.8: T-02 to Buranagar, at CH. 6.90 km, Bhangar- I Block, Dist.-South 24 Parganas, W.B. Sl.No.9: T-06 to Sasari-169, at CH. 1.90 km, Baruipur Block, Dist.-South 24 Parganas, W.B. Sl.No.10: T-02 to Sasari-169, at CH. 3.80 km, Baruipur Block, Dist.-South 24 Parganas, W.B. To compare the experimental and presumptive design values of soaked CBR as per IRC:SP:72-2007, tested soils have been classified into different groups by using the reported values of LL and PI as per the plasticity chart and furnished in the Table 3. Further comparison has been made in between the experimental and predicted values of soaked CBR by following the guidelines of evaluating procedure of Nomograph from IRC:SP:72-2007, and the results are tabulated in the Table 4. From the Table 3, it is observed that experimental soaked CBR values determined at optimum moisture content of ML and CL group of soils have shown the lower amount compared to the typical presumptive design CBR values as specified in the IRC:SP:72-2007. But between two experimental values of soaked CBR of CL-ML group of soils, one value has satisfied the said design chart and other one remains below the lower limit. However the reported value of soaked CBR of CH group of soil exceeds the upper limit of the presumptive design CBR values as Fig. 1: Nomograph for Computing Soaked CBR Value From specified in the IRC:SP:72-2007. Sieve Analysis Data (CRRI, 1990) California Bearing Ratio, Evaluation and Estimation: A Study on Comparisons 21

Further for prediction of soaked CBR by using Table 3: Comparison Between the Typical Presumptive Design Nomograph as per IRC:SP:72-2007 as shown in the Table CBR Values and the Tested Values Reported in DPR 4, it is observed that the variation between the experimental Presumptive Design Reported values and the predicted values remains within the range Values As Per IRC:SP:72- Value of 1% to 49%. Among 10 nos. of predicted values, 50% Sl. 2007 have remained within limit of 20% and balance exceeds No. IS Reported IS Typical the same. Classific- Soaked Classific- Soaked Table 2: Physical Properties of Different Soils Reported ation CBR ation CBR in the DPR 1 ML 3.11 ML,MI,CL,CI 4-5 Soaked Sl. LL PL PI Type of Soil CBR No % % % 2 ML 3.39 ML,MI,CL,CI 4-5 (%) 3 CL 3.24 ML,MI,CL,CI 4-5 -23.2% 1 & 3.11 Non- Non- Non- -76.8% plastic plastic plastic 4 CL 3.55 ML,MI,CL,CI 4-5

Sand-26.7% 5 CL 3.62 ML,MI,CL,CI 4-5 2 Silt & 3.39 Non- Non- Non- Non- Clay-73.3% plastic plastic plastic 6 CL-ML 4.0 ML,MI,CL,CI 4-5

7 CL-ML 3.51 ML,MI,CL,CI 4-5 Sand-2.0% 3 Silt & 31.21 16.14 15.07 3.24 Clay-98.0% 8 CL 3.37 ML,MI,CL,CI 4-5

9 CH 3.22 CH, MH 2-3 Sand-11.56% 4 Silt & 31.0 16.21 14.79 3.55 Clay-88.44% 10 CL 3.52 ML,MI,CL,CI 4-5

Sand-10.21% Table 4: Comparison of the Predicted CBR Values from the 5 Silt & 30.70 17.22 13.48 3.62 Nomograph with the Tested Values Reported in DPR Clay-89.79% Reported Predicted Soaked CBR Sl. % Soaked By Nomograph No. Diff. Sand-4.0% CBR (%) As Per IRC:SP:72-2007 6 Silt & 29.23 22.83 6.40 4.0 Clay-96.0% 1 3.11 4.50 31

2 3.49 4.40 21 Sand-2.0% 7 Silt & 27.58 21.25 6.33 3.51 3 3.24 3.00 8 Clay-98.0% 4 3.55 3.50 1 Sand-1.0% 8 Silt & 29.27 20.11 9.16 3.37 5 3.62 3.40 6 Clay-99.0% 6 4.0 3.10 29

Sand-8.0% 7 3.51 2.35 49 9 Silt & 36.24 24.32 11.92 3.22 Clay-92.0% 8 3.37 2.30 47

9 3.22 3.25 1 Sand-4.0% 10 Silt & 34.57 22.74 11.83 3.52 10 3.52 3.10 14 Clay-96.0%

22 T.K. Roy, B.C. Chattopadhyay and S.K. Roy

4. CONCLUSION IS 2720. Method of Test for Soil (Part CVI). Laboratory From this experimental study, the following conclusions Determination of CBR. can be made: Karunaprema, K.A.K. and Edirisinghe, A.G.H.J. (2002). (i) Estimation of CBR on the basis of cheap and less Some Useful Relationships for the use of Dynamic Cone time consuming method will help the designers Penetrometer for Road Subgrade Evaluation. and constructors enormously. Proceedings of the Civil Engineering Society Annual (ii) However prediction of soaked CBR value by using Seminar, University of Peradeniya, Sri Lanka , 85. the presumptive design chart as specified in the Nuwaiwu, C.M.O., Alkali, I.B.K. and Ahmed, U.A., (2006). IRC:SP:72-2007 have shown significant difference Properties of Ironstone Lateritic in Relation to with the experimental values of the same. Road Pavement Construction. Geotechnical and (iii) By using Nomograph of IRC:SP:72-2007, the Geological Engineering, 24, 283-298. difference between the reported and predicted Roy T.K., Chattopadhyay B.C. and Roy S.K., (2006). soaked CBR values exceeds 20%, when soil is non- Prediction of CBR for Subgrade of Different Materials plastic or having very small amount of sand from Simple Test., Proc. International Conference on content. ‘Civil Engineering in the New Millennium – Opportunities and Challenges, BESUS, West REFERENCES Bengal,Vol.-III :2091-2098. Brown, S.F. (1996). in Pavement Shukla, S. K. and Kukalyekar, M. P., (2004). Development Engineering. Geotechnique, 46 (3), 383-426. of CBR Correlations for the Compacted Fly Ash. IRC: SP 72 (2007). Guidelines for the Design of Flexible Proceedings of the Indian Geotechnical Conference. Pavements for Low Volume Rural Roads. Warangal, 53-56. IS 2720 (Part V) (1985). Determination of Liquid & Plastic Srinivasa Rao, K. (2004). Correlation between C.B.R. And Limits. Group Index. Proceedings of the Indian Geotechnical IS 2720. Method of Test for Soil (Part VIII) (1980) Conference. Warangal, 477-480. Laboratory Determination of Moisture Content & Dry Density.